This application relates generally to fiber-optic communications and more specifically to techniques and devices for routing optical signals to different output ports (or, conversely, routing different spectral bands at the output ports to the input port).
The Internet and data communications are causing an explosion in the global demand for bandwidth. Fiber optic telecommunications systems are currently deploying a relatively new technology called dense wavelength division multiplexing (DWDM) to expand the capacity of new and existing optical fiber systems to help satisfy this demand. In DWDM, multiple wavelengths of light simultaneously transport information through a single optical fiber. Each wavelength operates as an individual channel carrying a stream of data. The carrying capacity of a fiber is multiplied by the number of DWDM channels used. Today DWDM systems employing up to 80 channels are available from multiple manufacturers, with more promised in the future.
In all telecommunication networks, there is the need to connect individual channels (or circuits) to individual destination points, such as an end customer or to another network. Systems that perform these functions are called cross-connects. Additionally, there is the need to add or drop particular channels at an intermediate point. Systems that perform these functions are called add-drop multiplexers (ADMs). All of these networking functions are currently performed by electronicsxe2x80x94typically an electronic SONET/SDH system. However SONET/SDH systems are designed to process only a single optical channel. Multi-wavelength systems would require multiple SONET/SDH systems operating in parallel to process the many optical channels. This makes it difficult and expensive to scale DWDM networks using SONET/SDH technology.
The alternative is an all-optical network. Optical networks designed to operate at the wavelength level are commonly called xe2x80x9cwavelength routing networksxe2x80x9d or xe2x80x9coptical transport networksxe2x80x9d (OTN). In a wavelength routing network, the individual wavelengths in a DWDM fiber must be manageable. New types of photonic network elements operating at the wavelength level are required to perform the cross-connect, ADM and other network switching functions. Two of the primary functions are optical add-drop multiplexers (OADM) and wavelength-selective cross-connects (WSXC).
In order to perform wavelength routing functions optically today, the light stream must first be de-multiplexed or filtered into its many individual wavelengths, each on an individual optical fiber. Then each individual wavelength must be directed toward its target fiber using a large array of optical switches commonly called an optical cross-connect (OXC). Finally, all of the wavelengths must be re-multiplexed before continuing on through the destination fiber. This compound process is complex, very expensive, decreases system reliability and complicates system management. The OXC in particular is a technical challenge. A typical 40-80 channel DWDM system will require thousands of switches to fully cross-connect all the wavelengths. Opto-mechanical switches, which offer acceptable optical specifications, are too big, expensive and unreliable for widespread deployment. New integrated solid-state technologies based on new materials are being researched, but are still far from commercial application.
Consequently, the industry is aggressively searching for an all-optical wavelength routing solution that enables cost-effective and reliable implementation of high-wavelength-count systems.
Embodiments of the invention are directed to a method and optical routing apparatus for directing an optical signal. The optical routing apparatus includes an input port configured to provide the optical signal along an incident path and a plurality of output ports configured to receive the optical signal. An optical switching arrangement is operated to route the optical signal from the input port to one of the output ports depending on the configuration of the optical switching arrangement.
The optical switching arrangement includes a plurality of fixed mirrors, each of which is positioned with respect to the incident path of the optical signal at a particular angle. Each fixed mirror is associated with one of the output ports. The optical switching arrangement also includes a rotatable mirror configured to rotate to a plurality of distinct positions that define the different configurations of the optical switching arrangement. In each of those positions, the rotatable mirror defines an approximately right included angle with a particular fixed mirror. The optical path defined by that position includes a reflection of the rotatable mirror and off that particular fixed mirror.
In various embodiments, the lengths of the optical paths from the input port to the output ports are of approximately the same length. In another embodiment, the fixed mirrors are positioned specifically to achieve equalization of path length. The size of the fixed mirrors may vary to account for dispersion of the optical signal off the rotatable mirror, with each fixed mirror having a spatial extent proportional to its distance from the rotatable mirror. In particular embodiments, the number of output ports and fixed mirrors is two, thereby defining a 1xc3x972 optical switch. In some such embodiments, the included angles defined by the rotatable mirror and the two fixed mirrors are complementary.